Vacuum powered multiple document detector



April 7, 1970 M. SILVERBERG 3,504,911

VACUUM POWERED MULTIPLE DOCUMENT DETECTOR Filed Oct. 25, 1967 2 Sheets-Sheet 1 INVENTOR.

MORTON SILVERBE BY M ATTORNEYS I p 7, 197 0 MQSILVERBERG 3,504,911

VACUUM TowEREb MULTIPLE DOCUMENT DETECTOR Filed Oct. 25, 1967 2 Sheets-Sheet z HI II H II HHTH HHT T .m mml IIIHILLlLlJJH Ilium 14 l MOT- i INVENTOR. MORTO SILV RBE G I l BY ATTORNEYS United States Patent York Filed Oct. 25, 1967, Ser. No. 678,059

Int. Cl. B65h 3/46 US. Cl. 271-56 9 Claims ABSTRACT OF THE DISCLOSURE Apparatus for detecting sheets advanced in a superposed relationship along a path of travel in which a pair of opposed plate members form a passageway through which sheets are advanced. Port means laterally positioned in the plate members distribute an applied vacuum within the passageway, the port means being longitudinally positioned in the plate members to provide an area of high pneumatic resistance within the passageway between the entrance thereof and the port means, and an area of loW pneumatic resistance within the passageway between the exit thereof and the port means. Vacuum is applied to the passageway through the port means via a manifold connected to a supply source. Ambient air enters the passageway to fill the vacuum from the sheet exit end due to the low pneumatic resistance thereat which serves to separate superposed sheets. Superposed sheets thus separated are drawn against the port means causing a decrease in pressure in the respective manifold lines. Pressure responsive switch means operative in response to this change in pressure, condition an electrical circuit to control the advancement of sheets along the path of travel.

BACKGROUND OF THE INVENTION This invention relates generally to sheet detecting apparatus and more particularly to apparatus for detecting the passage of multiple sheets in a sheet handling operation.

In sheet handling operations of the type wherein a sheet or document is transported from one station to another, it may often be desirable or necessary to insure against the passage of more than a single sheet at a time. This is especially true in machines of the type disclosed in copending application Ser. No. 632,662 filed Apr. 21, 1967 in the names of Gordon P. Taillie, John F. Gardner, Thomas B. Michaels and Donald W. Gouldsmith, wherein xerographic images are formed in reduced configuration on electrical accounting machine cards.

In the particular machine referred to above, a document to be imaged is advanced from a stacked relationship to a document registration gate by a sheet feeding device of the type disclosed in copending application Ser. No. 632,793, filed Apr. 21, 1967, in the names of Klaus K. Stange, Adalbert A. Lux and Thomas B. Michaels.

Thereafter, a document is released by the registration gate and transported into the optical path for imaging by a document conveyor or transport apparatus of the type disclosed in copending application Ser. No. 632,801 filed Apr. 21, 1967, in the names of John F. Gardner, Martin H. Lustig, and Adalbert A. Lux.

In such a sheet handling operation, it is extremely important that not more than a single document be fed to the conveyor for imaging at a time. This is to prevent double exposures due to the translucent properties of some, paper stocks, mis-registration of documents with the registration gate and jams which may result with a consequent loss of time to remove the difficulty.

Numerous attempts to provide multiple sheet detectors have not proven entirely satisfactory. For example, it is known in prior multiple sheet detectors to utilize a mechanism which measures or calipers the thickness of sheets passing along the path. Where one or more documents pass in a folded or overlapping relationship, the additional thickness is sensed and the advancing mechanism is stopped by either mechanical or electromechanical means. In a similar manner optical and electrical sensing mechanisms have been utilized to detect the passage of more than a single document. These devices while effective in some operations do not always prove satisfactory due to the precise settings and adjustments required, and due to variations in paper thickness.

Another approach to detecting multiple documents or sheets has been the utilization of pneumatic devices. Some such devices utilize a pair of opposed vacuum ports between which sheets are advanced. When more than a single sheet is advanced between the ports, one sheet is drawn against the adjacent port and another sheet is drawn against the opposite port. This action is then utilized to stop the sheet advancing mechanism until the multiple sheets are removed.

A prime disadvantage of the previously described vacuum detector has been the ineffectiveness in operation and the failure to detect multiple sheets. This is due primarily to the fact that as a practical matter, the vacuum ports are not effective to separate the sheets from the overlapping relationship due to the perviousness of the sheets themselves and the tendency to adhere together in a slug or stack.

To overcome this difiiculty, devices which utilize both negative and positive air pressures have been proposed. These devices in addition to an opposed vacuum port system utilizes a source of pressurized air which is directed at the leading edge of advancing documents to obtain separation of the stacked sheets. After separation by the pressurized air the separated sheets are drawn against the vacuum ports to stop the advancing mechanism. While these devices have proven more effective than the prior vacuum detectors, they are more expensive and more complex by requiring additional apparatus to obtain effective separation.

SUMMARY OF THE INVENTION Accordingly, it is a primeobject of the invention to detect multiple sheets in a sheet advancing system.

Another object of the invention is to provide multiple document detection apparatus which is effective in operation.

Yet another object of the invention is to provide improved multiple document detection apparatus of the vacuum type.

Still another object of the invention is to provide improved multiple sheet detection apparatus which is eflective in detecting sheets of mixed length, width, thickness, and weight.

A further object of the invention is to improve the sheet separating characteristics of vacuum operated multiple sheet detectors.

Still a further object of the invention is to provide improved pneumatic multiple sheet detection apparatus which obviates the necessity of an independent sheet separation means.

These and other objects of the invention are attained by means of a first and second opposed plate members which form a passageway through which sheets are advanced along the path of travel, and port means laterally positioned in the plate members to distribute an applied vacuum within the passageway, the port means being longitudinally positioned proximate to the exit edges of the plate members to provide an area of high pneumatic resistance within the passageway between the entrance thereof and the port means, and a area of low pneumatic resistance within the passageway between the exit thereof and the port means. A vacuum is applied to the passageway through the port means via a manifold connected to a supply source. As a result of the high pneumatic resistance at the entrance end, air enters the passageway through the exit end in response to the vacuum pressure to separate superposed sheets located therein.

Pressure responsive switch means operative in response to a change of pressure in the manifold as the result of the presence of multiple sheets in the passageway, condition an electrical circuit to control the advancement of sheets along the path of travel.

Other objects of the invention will become readily apparent to those skilled in the art in view of the following detailed disclosure and description thereof, especially when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional view of the sheet separating and sensing apparatus according to the present invention.

FIG. 2 is a cross sectional view of the sheet separating and sensing apparatus according to the present invention illustrating a single sheet in sensing position.

FIG. 3 is a cross sectional view of the sheet separating and sensing apparatus according to the present invention illustrating multiple sheets in the sensing position.

FIG. 4 is an elevational view of the sheet separating and sensing apparatus according to the present invention taken along the lines 44 of FIG. 1.

FIG. 5 schematically illustrates a multiple sheet detection system as contemplated by the present invention.

FIG. 6 illustrates the sheet separating and sensing apparatus according to the present invention as adapted for use in an automatic sheet advancing device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIGS. 1-4, there is illustrated a sheet separating and detecting head generally designated 10, as contemplated by the present invention. As shown in FIGS. 1-3, rotatably mounted pinch rollers such as 24-25 and 26-27 may be arranged in pairs to define a path of travel between which sheets are advanced in a sheet handling operation. The sheet separating and detecting head 10 includes a pair of plate members 12 and 13 which are positioned adjacent the path of travel generally parallel thereto in an opposed spaced relationship. Plate members 12 and 13 preferably extend transversely across the path of travel and longitudinal thereto to provide a passageway through which sheets are advanced from one set of pinch rollers to the other. A plurality of apertures or port members 14 are laterally positioned in plate members 12 and 13 across the path of travel as may be seen in connection with FIG. 4. Port members 14 are positioned longitudinally in plate members 12 and 13 along the path of travel as may be seen in connection with FIGS. 1-3. As shown in FIGS. 1-3, port members 14 are substantially spaced from the sheet entrance end of the passageway formed by plate members 12 and 13 and in close proximity to the sheet exit end of the passageway, the purpose of which will hereinafter be more fully explained.

A pair of curved or arched plate members 16 and 17 are connected to plate members 12 and 13 respectively and serve to define a vacuum chamber extending vertically from plate members 12 and 13 and surrounding port members 14. A pair of side plates 18 and 19 connected to plate members 12-13 and 16-17 complete the enclosure chambers about plate members 12 and 13 and provide a lateral guide and enclosure for the passageway between plate members 12 and 13.

Vacuum is supplied to the respective chambers of sheet separator and detector head 10 by means of an air pump 31. Air pump 31 may be driven by a suitable power source such as MOT-1. Vacuum pressure from air pump 31 is conducted to port members 14 in plate member 12 and 13 via vacuum conduits 33 and 34 connected to the respective surrounding chambers.

A pair of pressure responsive switches or pneumatically operated relays 32 and 35 of a type which are generally well known are connected to vacuum conduits 33 and 34 to be actuated in response to a change of pressure therein.

An electromagnetically actuated clutch or brake assembly 38 such as schematically illustrated in connection with FIG. 5 may be utilized to control the advancement of sheets along the path of travel. As schematically illustrated in FIG. 5, clutch assembly 38 is operated to interrupt advancement of sheets in response to a high level signal from the output terminal of AND gate G-1 via amplifier AMP-1. With the relays 32 and 35 open as shown in FIG. 5, a low level signal is supplied to the input terminals of AND gate G-l thus resulting in a low level signal at the output terminal of G-l. With one of the relays 32 or 35 closed and the other open, a high level signal is provided at the respective input terminal of 6-1 to which the closed relay is connected and a low level signal is provided at the respective input terminal to which the open relay is connected thus resulting in a low level signal at the output terminal of G-l. With both of the relays 32 and 35 closed, a high level signal is provided at each of the input terminals of 6-1 thus resulting in a high level signal at the output terminal, which high level signal alters the condition of clutch assembly 38. Thus the operating condition of clutch assembly 38 is changed only in response to a change in condition of both relays 32 and 35.

With the electrical circuitry conditioned as shown in connection with FIG. 5, a sheet 21 may be advanced between the plate members 12 and 13 as seen in FIG. 2. As ambient air is drawn into the respective vacuum chambers surrounding plate members 12 and 13 through the port members 14, the single sheet may be drawn against one of the sets of port members, for example, those in plate member 12. As sheet 21 is drawn thereagainst, inhibiting but not completely interrupting the air fiow through conduit 33, a drop in pressure within the surrounding vacuum chamber and vacuum conduit 33 is experienced. This change in pressure effects activation of pneumatic relay 32 closing the respective circuit and providing a high level signal at the input terminal of AND gate G-l. This however does not alter the condition of clutch assembly 38 due to the unchanged low level signal which is provided at the output terminal of AND gate G-l. With the circuit thus conditioned the single sheet 21 is uninterruptedly advanced by the advancing mechanism through the passageway and into the succeeding pinch rollers 26-27. As the sheet passes from the passageway and engagement with port members 14, a rise of pressure within vacuum conduit 33 is experienced which returns the circuit to the condition as shown in FIG. 5.

With the electrical circuitry again conditioned as shown in connection with FIG. 5, a plurality of superposed sheets such as 21-22 may be advanced between the plate members 12 and 13 as seen in FIG. 3. As ambient air is drawn into the respective vacuum chambers surrounding plate members 12 and 13 through the port members 14, the superposed sheets 21-22 may be drawn, for example, firstly against one of the sets of port members such as those in plate member 12. As was described in connection with a single sheet, a drop in pressure within the surrounding vacuum chamber and vacuum conduit 33 is experienced. This change in pressure effects activation of pneumatic relay 32 closing the respective circuit and providing a high level signal at the input terminal of AND gate G-l.

It will be appreciated that the previously described positioning of port members 1-4 in plate members 12 and 13 is a critical factor according to the present invention. The positioning of port members 14 in plate members 12 and .13 provides an area of low pneumatic resistance between the sheet exit end of the passageway and the port members, and an area of high pneumatic resistance between the sheet entrance and of the passageway and the port members. Because of this difference in pneumatic resistances, a substantially larger volume of the ambient air which is drawn through port members .14, is drawn into the passageway from the sheet exit end rather than the sheet entrance end. This high volume of entering ambient air is effectively utilized to separate the superposed sheets for reliable detection.

With sheets 21 and 22 drawn against the port members in plate member 12, the sheets are advanced in contact therewith toward the exit end of the passageway. It should be noted that although the port members may be covered by one or more sheets, the flow of air through the port members is not completely interrupted due to the porosityof the paper stock. Although the superposed sheets may be drawn and held against port members 14, this does not substantially interfere with the advancement of sheets through the passageway due to drag effects because of the location of port members 14 and the relatively low pressure differential utilized. Thus, as the leading edges of superposed sheets are advanced toward the exit end of the passageway, the incoming ambient air serves to separate the sheets from the superposed condition. The total extent of the forces exerted on the superposed sheets by the incoming ambient air is not known. However, the air flow as a result of the short distance through which it flows from the exit end of the passageway to the port members is believed to remain in a somewhat turbulent flow pattern. This may be the result of a flow pattern which is generated as the ambient air first converges to enter the exit end of the passageway and then diverges to pass through the port members without an extended flow within the passageway. In any event, the air flow thus created in the passageway separates the leading edges sufiiciently to allow air to enter between the sheets, forcing sheet 22, for example, away from plate member 12 and against port members 14 in plate member 13.

With sheet 21 in engagement with the port members in plate member 12, and sheet 22 in engagement with the port members in plate member 13, both of the relays 32 and 35 are actuated, closing the respective circuits. With both circuits closed, a high level signal is supplied to the input terminals of AND gate G-l providing a high level signal at the output terminal of gate G1 which is then utilized to condition clutch member 38 in response thereto.

In a preferred version of the invention with a passageway having a longitudinal length, on the order of two inches, a linear array of approximately one-sixteenth inch diameter port members spaced approximately on onesixteenth inch centers and one-quarter inch from the exit edge of the passageway produces effective separation of superposed sheets therein. This arrangement has additionally been found to optimize the drag effect exerted on the sheets as they are advanced across the port members. This arrangement thus provides a simple and inexpensive, yet effective and reliable means for detecting the passage of multiple sheets in a sheet handling operation.

Referring to FIG. 6, the sheet detecting apparatus according to the present invention is particularly adapted for use in connection with sheet feeding apparatus of the type disclosed in copending application Ser. No. 632,793. In such devices, sheets are singularly advanced for imaging in a xerographic machine by means of a friction drive wheel 41 engaging the top portion of an adjustably supported stack of sheets 42. Sheets from the top of the stack are advanced by the friction drive wheel 41 into the wrap formed between a stationary retarding roll or abutment member 43 which is in substantial contact with the moving surface of a belt member 44. Adhering overlapping sheets are separated by the abutment member as they are advanced through the wrap. The uppermost sheet in the wrap is advanced by the belt member 44 through the passageway between plate members 12' and 13 to engage a sheet interrupter 45 before being released to a pair of continuously rotating friction rolls 4647 which deliver the sheet to the moving transport 48 of the xerographic machine.

In the event that more than a single sheet is advanced into the passageway between plate members 12 and 13, the uppermost sheet therein is drawn against the port members in plate member 12 and the lowermost sheet therein is drawn against the port members in plate member 13 in the manner as previously described. With the uppermost and lowermost sheets in engagement with the respective port members in plate members 12 and 13, the electrical circuitry is conditioned to provide a high level signal at the output terminal of AND gate G-l in the, manner as previously described. In this embodiment, the output terminal of AND gate G-1 is connected to an input terminal of a gate circuit which controls the release of sheet interrupting member 45. This arrangement inhibits the release of sheet interrupting member 45 and hence the release of an engaged document to the pinch rolls 4647 in the event that more than a single sheet has been advanced through the passageway between plate members 12 and '13.

From the foregoing description, it may be seen that there is provided an improved means for separating and detecting the passage of multiple superposed sheets in a sheet handling operation.

While the invention has been described with reference to the structure disclosed herein, it will be understood that various modifications may be made without departing from the spirit of the invention, and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims.

What is claimed is:

1. Apparatus for detecting sheets advanced in a superposed relationship along a path of travel including,

means defining a passageway through which sheets are advanced,

port means positioned within said passageway to dis tribute an applied vacuum therein, said port means being further positioned in said passageway to provide an area of high pneumatic resistance between the entrance end of said passageway and said port means, and an area of low pneumatic resistance between the exit end of said passageway and said port means,

vacuum supply means for creating at least a partial vacuum,

manifold means operatively connecting said vacuum supply means and said port means to conductively apply a partial vacuum to said passageway,

means for interrupting the advancement of sheets along the path of travel, and

circuit means for operatively controlling said interrupting means in response to a set of predetermined conditions.

2. Apparatus according to claim 1, said circuit means including logic means for providing enabling and disabling pulses to said interrupting means.

3. Apparatus according to claim 2, said circuit means further including pressure responsive switch means oper able in response to a change of pressure within said manifold means to condition said logic means.

4. Apparatus for detecting sheets advanced in a superposed relationship along a path of travel including,

a pair of opposed plate members forming a passageway through which sheets are advanced,

port means laterally positioned in said plate members to distribute an applied vacuum within said passageway, said port means being further positioned longitudinally in said plate members to provide an area of high pneumatic resistance within said passageway between the entrance end of said passageway and said port means, and an area of low pneumatic resistance within said passageway between the exit end of said passageway and said port means, vacuum supply means for creating at least a partial vacuum, manifold means operatively connecting said vacuum supply means and said port means to conductively apply a partial vacuum to said passageway, means for conditionally interrupting the advancement of sheets along the path of travel, and circuit means for operatively controlling said interrupting means in response to a set of predetermined conditions. 5. Apparatus according to claim 4, said circuit means including,

pressure responsive switch means operable in response to a change of pressure within said manifold means, and logic means conditionally responsive to said switch means for enabling and disabling said interrupting means. 6. Apparatus for detecting sheets advanced in a superposed relationship along a path of travel including,

first and second plate members in an opposed spaced relationship forming a passageway through which sheets are advanced along said path of travel, port means in said plate members laterally positioned across said path of travel to distribute an applied vacuum within said passageway, said port means being further positioned longitudinally along said path of travel in said plate members to provide an area of high pneumatic resistance within said passageway between the entrance end of said passageway and said port means, and an area of low pneumatic resistance within said passageway between the exit end of said passageway and said port means, vacuum supply means for creating at least a partial vacuum, vacuum manifold means operatively connecting said vacuum supply means and said port means to conductively apply a partial vacuum to said passageway, means operative to interrupt the advancement of sheets along the path of travel, and circuit means for controlling said interrupting means in response to a set of predetermined conditions. 7. Apparatus according to claim 6, said circuit means including,

conditionally responsive logic means for maintaining said sheet interrupting means in a sheet engaging position, and

switch means operative in response to a change of pressure within said manifold means for conditioning said logic means.

8. In a multiple sheet detecting apparatus of the vacuum type, a sheet separating and detecting head comprising,

means defining a passageway through which sheets are advanced, and

port means laterally positioned within said passageway to distribute an applied vacuum therein, said port means being spaced longitudinally within said passageway to provide an area of high pneumatic resistance between the entrance end of said passageway and said port means and an area of low pneumatic resistance between the exit end of said passageway and said port means.

9. Apparatus for detecting sheets advanced in a superposed relationship along a path of travel including,

first and second plate members supported in an opposed spaced relationship to form a passageway through which sheets are advanced along said path of travel,

port means in said plate members laterally positioned across said path of travel to distribute an applied vacuum within said passageway, said port means being further positioned longitudinally along said path of travel in said plate members to provide an area of high pneumatic resistance within said passageway between the entrance end of said passageway and said port means, and an area of low pneumatic resistance within said passageway between the exit end of said passageway and said port means,

vacuum supply means for creating at least a partial vacuum,

vacuum manifold means operatively connecting said vacuum supply means and said port means to conductively apply a partial vacuum to said passageway and effect an influx of ambient air into said passageway, the high pneumatic resistance presented at the entrance end of said passageway and the low pneumatic resistance presented at the exit end of said passageway causing said influx of ambient air to substantially occur at said exit end of said passageway, said influx of ambient air at said exit end of said passageway engaging the leading edges of advancing superposed sheets to cause a separation thereof, one of the separated sheets being drawn against the port means in one of said plate members and the other of the separated sheets being drawn against the port means in the other of the plate members,

means operative to interrupt the advancement of sheets along the path of travel,

conditionally responsive logic means for maintaining said interrupting means in a sheet engaging condition, and

switch means operative in response to a predetermined change of pressure within said manifold means to condition said logic means and maintain said interrupting means in a sheet engaging condition.

References Cited UNITED STATES PATENTS 2,992,822 7/1961 Fraidenburgh 271-57 2,994,528 8/1961 Hull et al 27156 3,212,775 10/1965 Taylor 271-74 RICHARD AEGERTER, Primary Examiner 

